User manual

AMP2-VS and AMP2-VSA User Manual P/N 821583 Rev-A Section 3: Technical Information

SDI D/A Gain Calibration Fine Adjustment (919068 PCB)

The digital gain calibration is set at the factory for +4 dB (analog) = -20 dBFS (digital). Three other values (+8 = -20, +6 = -9, and

0 = -18) may also be user selected via a DIP switch on the rear panel (Item C, page 12). However, if a fine adjustment of the calibration

is desired, perform the following procedure:

1) Remove the top cover (3 screws along rear, 2 screws along front, 2 screws on each side, and one screw at center top).

2) Locate the trim pots (P1-P4) on the 919068 PCB (see Figure-3a below for trim pot locations).

3) Connect a digital (SDI) source embedded with audio of known digital amplitude and set the unit’s controls to monitor that source.

For convenience sake, it would be best to use your facility’s digital reference level, but any nearby level may be used with

appropriate scaling of output level required.

4) Using an accurate DMM (preferably one having direct reading in dBv/dBu), measure the level on the Analog Out From SDI

phoenix connectors (Item B, page 12). Be sure to make measurement of the FULL balanced output, NOT just between one of

the outputs and ground!

5) Locate trim pots P5, P6, P7, and P8 (see Figure-3a below). Adjust P8 (channel 1) through P5 (channel 4) for the desired analog

level corresponding to the digital signal amplitude being supplied to the unit. For example, if your “house” Analog/Digital

correspondence is for a -18 dBfs digital level to correspond to an analog level of +0 dBu, it would be easiest to set the digital

source to -18 dBfs, set the gain calibration DIP switch for -18 dBFS = 0 dBu and then set P1 through P4 for 0 dBu outputs

on the phoenix Analog Output connectors. But, if a digital source of -20 dBfs is applied, even though the facility references are

for -18 dBfs, then the analog output levels should be adjusted for a -2.0 dBu analog output level on the phoenix connectors.

Note: If the meter being used to measure the analog outputs is not so accurate at those relatively low signal levels, you may wish to

increase the digital signal amplitude by some convenient factor like 10 dB or even 20 dB, but do not increase above digital full scale.

P5 - Adjusts Channel 4

P6 - Adjusts Channel 3

P7 - Adjusts Channel 2

P8 - Adjusts Channel 1

Figure-3a:

SDI to Analog Module PCB (919068)

D/A Gain Calibration Trim Pot Locations

Note: Turning pots counter-clockwise

(CCW) increases the analog audio

output level.